Hydrologic History Research Articles

Groundwater Flow to Gale Crater in an Episodically Warm Climate

AbstractOrbiter and rover data have revealed a complex and intermittent hydrological history in Gale Crater on Mars, where habitable environments appear to have endured for at least thousands of years. The intermittency may be the result of a dominantly cold climate punctuated by geologically brief periods of warmth and active hydrology. However, the time required to establish an integrated hydrological cycle in a warming climate is difficult to ascertain and has not been thoroughly investigated. Here we model the transient evolution of groundwater flow and subsurface temperature, the slowest evolving components of the hydrological cycle, during a warm departure from cold conditions. We find that tens of thousands of years are likely required before groundwater could be a meaningful source for large lakes in Gale. With highly favorable conditions, primarily high permeability, significant flow might develop in thousands of years. This implies that surface water dominates during the beginning of a warm phase. Annual mean surface temperatures in Gale below 290 K would likely leave the nearby highlands frozen at the surface. In that case, deep aquifers beneath a highlands permafrost layer could deliver water to Gale, where low temperatures would have reduced evaporation.

New insights into Holocene hydrology and temperature from lipid biomarkers in western Mediterranean alpine wetlands

Alpine regions of the Mediterranean realm are among the most climatically sensitive areas in the world. Thus, alpine wetlands from the southern Iberian Peninsula, in the westernmost part of the Mediterranean region, are highly sensitive sensors of environmental changes. Difficulties have surfaced in separating controls by temperature and/or precipitation in previous paleoenvironmental studies from alpine environments in this area. We present a Holocene biomarker record (n-alkanes and long-chain diols) from a high elevation lake, Laguna de Río Seco (LdRS), in the south of the Iberian Peninsula, which contributes to the identification of these forcing mechanisms. The hydrological history of the area, primarily water availability and evapotranspiration, is reconstructed by means of the n-alkane record, including the indices of average chain length, portion aquatic, and carbon preference index, as well as hydrogen isotopes (δD) of aquatic (δDaq) and terrestrial (δDwax) n-alkanes. Temperatures are also estimated using the algae derived long-chain diols. We interpret δDaq and δDwax fluctuations as showing changes in the source and amount of precipitation throughout the LdRS record. An Atlantic precipitation source appears to have predominated during the early-middle Holocene, but an occasional Mediterranean influence with an isotopic enrichment in precipitation is detected in the middle-late Holocene that is likely related to the setting of the current atmospheric pattern in southeastern Iberia under the joint control of the North Atlantic Oscillation (NAO) and the Western Mediterranean dynamics, such as the Western Mediterranean Oscillation (WeMO). Our new record from LdRS is consistent with a generalized trend of a humid early-middle Holocene with low temperature variability, evolving towards an arid middle-late Holocene with abrupt temperature changes. In addition to these long-term trends during the last ∼10,500 years, two phases of climate instability, evidenced by abrupt depletions in δDaq, have been identified at the end of these periods, one between ∼6500 and 5500 cal yr BP and another in the last ∼500 years. These episodes would represent strengthened winter cold conditions that favoured the persistence of snowpack and frozen soil in the catchment, causing reduced terrestrial plant growth and low lake evaporation. According to the long-chain diol record, temperatures during these phases were relatively low, but experienced abrupt increases at the end of each period.

Hydrologic Correlates of Reproductive Success in the Alligator Gar

AbstractPrevious work relating adult age data to historic hydrology indicated that strong year‐classes of Alligator Gar Atractosteus spatula were rare, tied to major flooding events, and linked to the inundation and connectivity of floodplain habitats. Although spawning habitat suitability criteria have been correlated with successful recruitment in Texas Alligator Gar populations, direct evaluation of recruitment documenting young‐of‐the‐year (age‐0) presence or abundance has not been reported. To specify conditions associated with successful spawning and recruitment of Alligator Gar, we sampled for age‐0 fish monthly from May to July 2013–2017 in the Trinity River and from May to July 2015–2017 in Choke Canyon Reservoir. Suitability criteria predicted strong year‐classes in 2015 and 2016 for the Trinity River and in 2015 for Choke Canyon Reservoir; the predictions were confirmed by the presence of abundant age‐0 Alligator Gar in those systems and years. Hatch dates of juvenile Alligator Gar were estimated from otoliths and compared to corresponding environmental and hydrologic conditions. Hatch date analyses indicated a protracted spawning duration in 2015 associated with extended widespread flooding and a narrower range of spawning dates in 2016. Due to rapid growth and variable gear efficacy relative to fish size, multiple gears were required to assess the full size range of age‐0 Alligator Gar. A standardized sampling framework that included visual searching and floating mini‐fyke nets effectively sampled age‐0 Alligator Gar from 15 to 650 mm TL. We recommend a two‐tiered approach for predicting and monitoring Alligator Gar recruitment. First, the monitoring of hydrology and the application of suitability criteria can provide an early predictor of potential Alligator Gar reproductive success. If conditions are favorable for spawning, then sampling for age‐0 Alligator Gar can confirm recruitment and can give an indication of the spatial extent (visual searching) and relative abundance (visual searching and/or mini‐fyke nets) of successful reproduction.

Organic matter geochemical signatures of sediments of Lake Ngoring (Qinghai-Tibetan Plateau): A record of environmental and climatic changes in the source area of the Yellow River for the last 1500 years

The climate history of the source area of the Yellow River (SAYR) is important to understanding the pacing and processes of climate evolution on the northeastern Qinghai-Tibetan Plateau (QTP). To date, results of research in this alpine region are limited. Herein, we provide a first lacustrine record from the largest freshwater lake on the QTP that archives climatic and environmental variations in the SAYR for the last 1500 yr. The bulk organic carbon and nitrogen isotopic compositions (δ13Corg and δ15Ntot) are combined with atomic carbon/nitrogen (C/N) ratios to indicate that the sedimentary organic matter in Lake Ngoring originates from autochthonous algae and that the terrestrial input is minor. Comparison of the record of organic carbon isotope values with published records of ice accumulation rate (IAR) of Dunde and Guliya glaciers from the northern QTP, the total solar irradiance (TSI), δ18O variations in the Greenland ice core and biologically sensitive indicators (C37:4 alkenone, crenarchaeol and bGDGT concentrations) from Lake Qinghai indicate that variations in the δ13Corg values in Lake Ngoring sediments reflect lake level fluctuations that are associated with variations in the amount of precipitation and glacier meltwater on the SAYR. High lake level phases indicated by positive shifts of δ13Corg values correspond to higher values of the North Atlantic Oscillation Index (NAOI) and lower values of the Southern Oscillation Index (SOIpr). This relation suggests that the hydrologic history in the SAYR is linked to changes in the Indian monsoon and the Westerlies and that both air masses delivered more moisture to the SAYR during high TSI stages. In contrast, variations in the δ15Ntot values resemble the multiple paleoclimate proxy records obtained from ice cores, peat sequences, lake sediments, and integrated paleo-records from other QTP sites, suggesting that the δ15Ntot values archived in Lake Ngoring sediments provide a history of past lake-water temperature variations that is consistent with the variation history of the temperature-dependent parameters from regional paleo-climatic studies. Global climatic events including the Dark Ages Cold Period, the Medieval Climate Anomaly, the Little Ice Age and Modern Warming in 20th century could be clearly observed in the δ15Ntot variations. In general, the δ13Corg and δ15Ntot values in Lake Ngoring sediments appear to be useful indicators for paleo-environment and paleo-climate reconstructions in alpine oligotrophic freshwater lakes such as this one.

Quantitative Analysis of Impact of Climate Variability and Human Activities on Water Resources Change in Suzhou City

Assessing the contribution of climate variability and human activities to Suzhou’s water resources change is important to the design of water resources and provide technical support for the overall planning of Suzhou sponge city. Based on Suzhou hydrology history data, Mann-Kendall method and linear regression method is used to study the change trend of more than 50 years of Suzhou rainfall runoff evaporation, coupled with Mann-Kendall method to validate the abrupt change point of the annual runoff series. The elasticity method is used to analysis the contribution of climate variability and human activities, to explore the main cause of the change of the runoff. The results show that the overall trend of rainfall over the years is increasing, the overall trend of runoff over the years is significantly increasing, and the overall trend of evaporation over the years is decreasing, and a sudden change occurred in 1991. climate variability in Suzhou is the main factor of runoff change, contributing 58.52% and contributing 41.48% to human activities.

A high-resolution climate history of geochemical and biological proxies from a tropical freshwater wetland located in the Kenyan Rift Valley

The sedimentary and biological material preserved in wetlands in semi-arid regions provide a rich repository of paleoclimate and paleoecological archives. These records reflect an underutilized, but typically ignored paleoenvironmental resource in semi-arid settings. The results presented here demonstrate that groundwater-fed wetlands constitute a valuable record of environmental change that not only complement reconstructions from lacustrine settings, but also contribute unique data and insights into climate and landscape change.We use data obtained from sediment cores collected from Loboi wetland, a groundwater-fed wetland located in the Equatorial East African Rift Valley of Kenya, to demonstrate the value of paleoenvironmental datasets extracted from wetland archives. This article relates surficial sedimentary geochemical data (TOC, δ13C, δ15N, C:N, and %C3) at Loboi to the extant macrophytic vegetation. The surficial data are used as an analog to interpret the geochemical signature of three sediment cores and a soil pit. The stratigraphic records show significant variation along a north to south transect through the wetland. The geochemistry indicates that papyrus wetland records are distinctly different from Typha dominated wetland sedimentary signatures. The interpretation of the stratigraphic material is further improved by the inclusion of sub-fossil macrophyte and testate amoebae remains. The extraction and identification of seeds of wetland plants from the sedimentary archive provide invaluable genus to species specific details of wetland ecology. Further, the inclusion of testate amoebae as an indicator of surface hydrological conditions has significantly improved interpretation of the hydrological history of Loboi wetland.The stratigraphic record from Loboi indicates that between ~1100 and 1470 C.E. (Medieval Climatic Anomaly) dry conditions dominated the Loboi region, except for a brief period of wetter conditions between ~1275 and 1345 C.E. Seasonally wetter conditions began to persist between ~1470 and 1630 C.E. Wetland sediments developed after this time as reflected by the sequestration of carbon in the sedimentary record. Recent historic biological and sedimentary proxies reflect increased agrarian impacts on the landscape surrounding Loboi.

A 1.68 Ma organic isotope record from the Hetao Basin, upper reaches of the Yellow River in northern China: Implications for hydrological and ecological variations

Abstract Quaternary hydrological and ecological variation of the paleolakes, intermittently developed within the Hetao Basin in North China, is not only closely related to the evolution of the Yellow River discharge but also influenced by the East Asian summer monsoon. However, long-term variability history of hydrology and ecology of these lakes, as well as the driving mechanism, is still poorly understood. Here, we reconstructed the hydrological and ecological variation of these paleolakes since the past ~1.68 Ma based on the interpretation of multi-geochemical proxies of the organic matter including TOC and TN concentrations, C/N ratios, and the δ13C and δ15N values. The results show that the lakes in the Hetao Basin are dominated by relative low lake level, deteriorated aquatic plant abundances and low phytoplankton productivity during the intervals ~1.47 to ~1.30 and ~1.17 to ~1.07 Ma, and ~0.68 to ~0.60 Ma, while relative high lake level with flourishing aquatic ecosystem and high aquatic productivity occurred from ~0.47 Ma to the last interglacial. Meanwhile, tectonically-driven relative height of the basin outlet, preventing the Yellow River water outflows the basin to widen the Yellow River channel in the basin, may be the key factor resulting in the significant rising of the water level of the paleolake formed within the Hetao Basin from ~0.47 Ma to the last interglacial.

Radiogenic isotope chemostratigraphy reveals marine and nonmarine depositional environments in the late Mesoproterozoic Borden Basin, Arctic Canada

Abstract The ca. 1050 Ma Bylot Supergroup in Arctic Canada is one of the best-preserved archives of late Mesoproterozoic geochemistry and biology and offers evidence that this period of Earth history may have been more biogeochemically dynamic than previously appreciated. The Bylot Supergroup was deposited in the Borden Basin and is the most thoroughly studied stratigraphic succession from a series of broadly contemporaneous late Mesoproterozoic intracratonic basins known as the Bylot basins. This ∼6-km-thick mixed carbonate-siliciclastic succession has undergone minimal postdepositional deformation and is now exposed on Baffin and Bylot Islands, Nunavut, Canada. Deep-water and tidally influenced carbonate facies, traditionally interpreted as marine, have yielded important insights into the evolution of Proterozoic seawater chemistry; however, more recent studies indicate that the Borden Basin was restricted marine or lacustrine for portions of its depositional history. Here, we present new multiproxy radiogenic isotope chemostratigraphic data spanning the Bylot Supergroup. A comparison of stratigraphic trends in radiogenic isotope data from hydrogenous (black shale 187Os/188Os and limestone 87Sr/86Sr) and detrital (whole-rock mudstone 143Nd/144Nd) sedimentary phases elucidates the complex hydrologic history of the Borden Basin and reconciles these disparate interpretations. Episodic coupling and decoupling between the composition of basin waters (from Os and Sr isotopes) and the local weathering input to the basin (from Nd isotopes) indicate that depositional environments within the Borden Basin fluctuated between marine and nonmarine (i.e., lacustrine). Variations in basin hydrology controlled secular sedimentation patterns through changes in basin water chemistry. These interpretations help to characterize the environment in which the early red algal fossil Bangiomorpha pubescens evolved. Episodically restricted epeiric seaways, such as within the Borden Basin, were relatively widespread within Rodinia and may have exerted unique selective pressures on eukaryotic evolution in the Mesoproterozoic Era. Hydrogenous and detrital radiogenic isotope chemostratigraphy, as implemented in this study, may provide a useful paleoenvironmental framework for future paleontological studies aimed at testing the role of freshwater environments in eukaryotic evolution. In addition, 87Sr/86Sr compositions from 81 new middle Bylot Supergroup marine limestone samples, calibrated by recent Re-Os geochronology, contribute to the terminal Mesoproterozoic marine 87Sr/86Sr curve. These data display a rise from ∼0.705 to 0.706 that reflects weathering of the active Grenville orogenic belt and demonstrates a global increase in chemical weathering during the amalgamation of Rodinia.

IAHS: a brief history of hydrology

Abstract. After describing the hydrological cycle and defining hydrology in the introduction, the early historical development of hydrology is briefly presented in the second section. Then the incorporation of hydrology within the IUGG and the subsequent development of the association are described chronologically. This description is organized into five sections corresponding to five different periods, focused on the scientific and organizational development of the association during each period. Finally, in the conclusions, the present state of the association is discussed together with an outlook for the future.

Runoff events and related rainfall variability in the Southern Carpathians during the last 2000 years

The occurrence of heavy rainfall events is expected to undergo significant changes under increasing anthropogenic forcing. South-eastern Europe is reacting rapidly to such changes, therefore understanding and forecasting of precipitation variability is vital to better comprehending environmental changes in this area. Here we present a sub-decadal reconstruction of enhanced rainfall events for the past 2000 years from the Southern Carpathians, Romania using peat geochemistry. Five clear periods of enhanced rainfall are identified at 125–250, 600–900, 1050–1300, 1400–1575 and 1725–1980 CE. Significant runoff is observed during the second half of the Medieval Warm Period, whilst the Little Ice Age was characterised by significant variability. The North Atlantic Oscillation appears to be the main control on regional precipitation, but changes in solar irradiance also seem to play a significant role, together with the Siberian High. Comparison of the data presented here with model outputs confirms the ability of models to predict general trends, and major shifts, but highlights the complexity of the region’s hydrological history.

Forensic Hydrology Reveals Why Groundwater Tables in The Province of Noord Brabant (The Netherlands) Dropped More Than Expected

Since the nineteen fifties, groundwater levels in the Netherlands dropped more than as simulated by hydrological models. In the rural sandy part of the Netherlands, the difference amounts to approximately 0.3 m on average. The answer to the question of what or who caused this ‘background decline’ of groundwater tables may have juridical and financial consequences, especially since Dutch farmers are entitled to financial compensation for crop damage caused by groundwater abstractions. In our forensic study, we investigated how anthropogenic changes in groundwater recharge from 1950 to 2010 affected groundwater levels. In this period, crop yields in agriculture have risen sharply, and, because crop water use is proportionate to crop production, this led to more crop evapotranspiration and subsequently less groundwater recharge. Urban expansion and forestation has also led to a decrease in groundwater recharge. We showed that these changes in recharge may have caused a decline of groundwater of 0.2–0.3 m over 60 years (1950–2010). The simulated drawdown caused by groundwater abstractions appeared to depend on the amount of groundwater recharge related to land use and crop yield. This means that to properly evaluate the effects of a particular groundwater abstraction, one should account for the hydrological history of the landscape since the start of that abstraction.

Sedimentary, geochemical and hydrological history of Lake Kinneret during the past 28,000 years

The sedimentary, geochemical and hydrological history of Lake Kinneret (Sea of Galilee) is reconstructed for the past ∼28 kyrs, based on three sedimentary cores drilled at the lake and a trench dug at the shore of the prehistorical Ohalo–II site. During the past 28 kyrs either laminated or massive fine-grained sediments were deposited in the lake comprising primary calcites and fine-grain detritus. Sr/Ca, Mg/Ca, 87Sr/86Sr ratios and δ18O values of live and fossil ostracod shells (Cyprideis torosa) and primary calcites together with XRD, grain-size, and carbonate content analyses indicate contribution of the following types of waters to the lake: (1) Jordan River; (2) Regional runoff; and (3) Ca-chloride brines (currently comprises the Tiberias Spa brine). During the last glacial period (∼28-24 ka) the lake rose to its highest stand of ∼170 m below sea level (bsl), expanding over the Kinnarot Basin and converging with the southern hypersaline Lake Lisan. At that time, waters were mainly supplied to the lake by the Jordan River and regional runoff with enhanced contribution of the Dead Sea Ca-chloride brine. Primary calcites were precipitated from the lake's solution forming sequences of laminated sediments on the lake's floor. At ∼24-22 ka (coinciding with Heinrich event H2 at the North Atlantic) the lake retreated below the modern level (of ∼214 m bsl), depositing mainly flood-related sediments at its margins. The lake slightly rose during the Younger Dryas and subsequently declined towards the modern level with decreasing contributions of the Jordan River waters, brines and regional runoff, reflecting a continuous aridification of the region during the Holocene.

Glaciovolcanism in the Tharsis volcanic province of Mars: Implications for regional geology and hydrology

The Tharsis region of Mars is a vast volcanic plateau which hosts the immense Tharsis Montes shield volcanoes. The Tharsis region is suggested by multiple lines of morphologic and modeling evidence to have been a site of coincident volcanic and glacial activity throughout the majority of the geologic history of Mars. The prolonged and overlapping histories of volcanism and glaciation within the Tharsis region raise the likelihood of widespread surficial glaciovolcanism, a possibility which is supported by the recognition of glaciovolcanic landforms in the region by past investigations. Given this likelihood, we perform an exploratory study to assess the potential role that surficial glaciovolcanism may have played in the geologic and hydrologic history of the Tharsis region. We first review the history and characteristics of volcanism and glaciation in the Tharsis region, as well as previously documented evidence for past glaciovolcanic activity, in order to outline relevant conditions and parameters. The outlined volcanic and glacial conditions are then used in conjunction with results and predictions from past modeling of surficial glaciovolcanic processes to assess the potential role of glaciovolcanism in the formation of the Tharsis region's major tectonic and hydrologic features. We conclude that surficial glaciovolcanism may plausibly have contributed to the formation of many of the tectonic and fluvial features in the Tharsis region, offering advantages over prior formation models, particularly for the large basin/chaos-sourced outflow channels concentrated in the area. The formation of a range of investigated features in the Tharsis region by surficial glaciovolcanism does not require ambient warm and wet climate conditions therefore suggesting potential consistency between the observed features and a predominantly cold and icy climate. Consequently, this analysis represents an incremental contribution to better understanding the climatic and hydrologic evolution of Mars. However, analyses performed in this work indicate that the glaciovolcanic origin models we considered are unable to viably account for the complete range of explored features, indicating that future work is required to better resolve the processes involved in their formation.

The impact of some anthropogenic activities on river Nile delta wetland ecosystems

The River Nile delta shallow lakes namely, Edku, Burullus and Manzala are natural wetland ecosystems, connected to fresh water sources at the south and to the open sea at the north. Throughout their relatively short geological and hydrological history, the lakes received unpolluted fresh water from the river Nile. Egyptians have begun practicing some form of water management for agriculture and transportation since about 5,000 years ago. As a result of agricultural and industrial development over the last century, the lagoons have been the end points of the last Egyptian use of the Nile water before flowing to the Mediterranean Sea; currently, the lakes receive fresh water from polluted drains inflow.

A global database of water vapor isotopes measured with high temporal resolution infrared laser spectroscopy

The isotopic composition of water vapour provides integrated perspectives on the hydrological histories of air masses and has been widely used for tracing physical processes in hydrological and climatic studies. Over the last two decades, the infrared laser spectroscopy technique has been used to measure the isotopic composition of water vapour near the Earth’s surface. Here, we have assembled a global database of high temporal resolution stable water vapour isotope ratios (δ18O and δD) observed using this measurement technique. As of March 2018, the database includes data collected at 35 sites in 15 Köppen climate zones from the years 2004 to 2017. The key variables in each dataset are hourly values of δ18O and δD in atmospheric water vapour. To support interpretation of the isotopologue data, synchronized time series of standard meteorological variables from in situ observations and ERA5 reanalyses are also provided. This database is intended to serve as a centralized platform allowing researchers to share their vapour isotope datasets, thus facilitating investigations that transcend disciplinary and geographic boundaries.

Flood hazard assessment of the Kashmir Valley using historical hydrology

Studies aimed at reconstructing the chronology of historical floods in a region assume an important role in flood hazard assessment, especially for flood prone regions like the Kashmir Valley. This is usually done through the review of historical documents and/or palaeohydrological studies; the latter allows access far beyond historical records. While as, archival scribes offer particularly valuable insights into attributes of hydrological extremes in the recent past. The Kashmir Valley has contours of its own in the field of historical hydrology, hitherto scattered across multiple textual scribes, making them obscure. Nevertheless, information collated and analysed made these contours visible in a specific way. The critical evaluation of historical flood records revealed that the Kashmir Valley was beleaguered with a series of catastrophic inundations. In addition, calibration of historical records against instrumental data spanning for ~1400 years were linked to quantifiable attributes to simulate their discharge, water surface elevation, and spatial extent using the Hydrologic Engineering Center's (HEC) River Analysis System (RAS) program. The deliverables of this study are expected to be valuable for flood hazard mitigation in the Kashmir Valley and for further research in this direction.

Statistical Analysis of Hydrological Regime of the Danube River at Ceatal Izmail Station

In the present study, we focused on the statistical analysis of changes in the characteristics of the minimum, average annual, and maximum discharge series of the Danube River at Ceatal Izmail water gauge. We have processed the series of annual average discharges during the whole water stage observation period 1840–2015, as well as the average daily discharge over the period 1931–2015. Firstly, we have identified changes in commonly used hydrological characteristics (such as long-term trends and variability of the annual averages, minimum annual discharges, occurrence of extremes, etc.). In the second part we divided the annual hydrogram of the daily discharges into individual flow events (waves) and we calculated their number and their duration in each year. Specifically, we have calculated the numbers and characteristics for extremely dry periods, as well as for small and large floods. The analysis of the discharge series of the Danube River evaluated at Ceatal Izmail shows: the long-term average discharge of the Danube River in the closing profile does not change. Annual regime has slightly changed - spring discharge peaks occur in the last years about 40 days earlier. From the statistical discharge analysis, we still do not know clearly whether this is the result of higher precipitation sums due to climate change or due to the channel training - reducing flood areas and draining acceleration. In the past, fluctuations in the Danube River flow were even higher than at present, in both directions - minimum and maximum discharge were more extreme in some periods. Therefore, it is necessary to focus on historical hydrology and analyze as many observations as possible. Statistical attention to the discharge, as well as precipitation and air temperature series needs to be continued.

Lake-level variability in Salar de Coipasa, Bolivia during the past ∼40,000 yr

AbstractVarious paleoclimatic records have been used to reconstruct the hydrologic history of the Altiplano, relating this history to past variability of the South American summer monsoon. Prior studies of the southern Altiplano, the location of the world’s largest salt flat, the Salar de Uyuni, and its neighbor, the Salar de Coipasa, generally agree in their reconstructions of the climate history of the past ∼24 ka. Some studies, however, have highly divergent climatic records and interpretations of earlier periods. In this study, lake-level variation was reconstructed from a ∼14-m-long sediment core from the Salar de Coipasa. These sediments span the last ∼40 ka. Lacustrine sediment accumulation was apparently continuous in the basin from ∼40 to 6 ka, with dry or very shallow conditions afterward. The fossil diatom stratigraphy and geochemical data (δ13C, δ15N, %Ca, C/N) indicate fluctuations in lake level from shallow to moderately deep, with the deepest conditions correlative with the Heinrich-1 and Younger Dryas events. The stratigraphy shows a continuous lake of variable depth and salinity during the last glacial maximum and latter stages of Marine Oxygen Isotope Stage 3 and is consistent with environmental inferences and the original chronology of a drill core from Salar de Uyuni.

A suite of macrophyte species distribution models for investigating hydrology-driven spatial changes in a large flood-pulsed tropical wetland

ABSTRACTSpatial ecological models of wetland systems are important tools for evaluating system response to changes in hydrological inputs, arising from anthropogenic manipulation or climate change. We present an approach using multiple species distribution models (SDMs) for floodplain macrophytes, based on empirical relationships with flood duration. 27 indicator species were identified for four floodplain classes in a seasonally pulsed distributary of the Okavango Delta, based on data from a field survey of 30 floodplain sites. Spatial hydrological history was constructed using a combination of Landsat and MODIS imagery, and ground-truthing. Relationships between duration and occurrence were used to construct general linear probability models (GLMs) of species along the hydroperiod gradient. The GLM parameters were then used to construct SDMs driven by a spatial hydrological model, which generates annual assessments of inundation duration in months in each 1km2 cell across the Delta. The modelled distribution fits were mostly robust (18 GLMs had p < 0.05). Tests of model performance against a validation set of five floodplain sites showed an average of 87% correct predictions of presence. The strong performance of the models and the ability to produce map-based and quantitative output indicate good potential for use in assessment of basin development scenarios.

Large-scale lava-ice interactions on Mars: Investigating its role during Late Amazonian Central Elysium Planitia volcanism and the formation of Athabasca Valles

The Central Elysium Planitia region contains evidence for large-scale, Late Amazonian volcanic and fluvial activity, the youngest on Mars. The region consists of a population of geologically recent, Late Amazonian-aged flood basalt volcanic plains which are incised by several large fluvial outflow channel systems. Recent understanding of the distribution of paleo-glaciation on Mars, informed by geomorphic indicators and model predictions, suggests that Central Elysium Planitia was an area of likely surface snow and ice accumulation throughout the Amazonian period. Furthermore, the volcanic plains of Central Elysium Planitia contain wide areas with preserved rootless cones, representing among the strongest evidence for past lava-ice interactions on Mars. Consequently, Central Elysium Planitia is of significant interest to understanding the recent Amazonian thermal and hydrologic history of Mars.Here we perform an exploratory assessment of the influence of surficial large-scale lava-ice interactions on the geomorphology of the Central Elysium Planitia volcanic plains and their potential contribution to the formation of the fluvial outflow channels contained within the region. The outflow channels of Central Elysium Planitia are generally interpreted to have formed as a result of catastrophic outbursts of groundwater released from pressurized, confined subsurface aquifers by magmatic dike emplacement. However, the formation of the relatively young Central Elysium Planitia outflow channels by this mechanism is subject to several demanding conditions which are not required of a lava-ice interaction origin. Therefore we revisit the origin of the Central Elysium Planitia outflow channels and explore large-scale lava-ice interactions as a possible alternative mechanism to contribute to, or account for, their formation. This assessment is performed through a case study of Athabasca Valles, a well-characterized outflow channel system which appears to emanate from the Cerberus Fossae fissure system.We find that surface ice and lava-ice interactions could have influenced the geomorphology of Central Elysium Planitia by contributing to the formation of the regions platy-ridged volcanic plains texture and rootless cones. Large-scale lava-ice interactions in Central Elysium Planitia are found to be able to readily supply the water volumes needed to form the Athabasca Valles system, but additional mechanisms are required to cause meltwater confinement and release to supply requisite discharges. Of the several potential mechanisms which could have led to meltwater confinement and release, the most likely are supra/englacial melt accumulation with outflow triggered by the flotation of a confining ice dam, and supra/englacial meltwater accumulation released by top-down supraglacial overflow. A simple analysis of these processes indicates that the rates of discharge necessary to form Athabasca Valles can be supplied while adhering to the geomorphic constraints of the system. Therefore, we conclude that the formation of the Athabasca Valles outflow channel system (and possibly other outflow channels in the region) could plausibly have been the result of surficial lava-ice interactions through meltwater confinement, accumulation, and release, providing an advantageous alternative to classical groundwater outburst models.